Rotary air impeller



Oct. 17, 1944. p, MULLER ETAL 2,360,440

ROTARY AIR IMPELLER Filed Jan. 26, 1942 Qttorney Patented Oct. 17, 1944 U N lT'ED STATES PAT ENT OFFICE ROTARY AIR IMPELLER Phillip A. Muller and Laclrlan W. Child, Detroit, Mich., assignorsto Evans'Products Company, Detroit, Mich., a corporation of Delaware Application January 26, 1942, Serial No. 428,208

5 Claims.

This invention relates to rotary impellers pri marily for moving air or gases, and. more particularly to a fan or blower of the conical or semi or axial centrifugal type. It is desired to have a single blower which may be used with good resuits to discharge into an axially extending passage or into laterally extending passages, or into passages at angles inbetween these.

It is an object of this. invention to provide a conical type of axial centrifugal blower, or fan which will be very silent in operation andyetwill give a high efficiency or high. static efficiencies over a rather wide range; of delivery volumes. Thatis, the curve of static efliciencies versus delivery volumes is. to have a relatively wide, sub.- stantially flat topped portion, and these: results to be had with av very low noise level throughout the operating range. More particularly, it is desired to have such a quiet blower which is. relatively small, compact and cheap, and to bev run at. relatively high speeds (for example, 2000' to 2500 R, P. M. for the hereinafter specifically disclosed nominal '7" size) ,and which will maintain its efficiency throughout a wide range of static operating pressuredifierences across the fan. For example, for the-nominal. 7- outer diameter size specifically disclosed herein, the pressure range may be from 0.01 to 0.6 inch of water, with the operative. pressure differences for the most usual applications being, from about /4.. to inch of water.

A further object. is to provide a silentv fan of this type which is cheap and compact andlends itself to mass production.

A further object. isto provide such a silent; cheap impeller which is. well adapted to be. used in a number of different applications, including various. heating" and ventilating uses in. vehicles, such as buses.

Further'and' more specific-objects are'to provide such a quiet. impeller which. may be. cheaply formed of sheet metal, including. steel, the inner. and outer blade-holding. members being readily spun or, preferably; drawn for. larger production, and the blades being cheaply punched by simple dies with a minimum of metal deformation and yet being well: stifiened; to; provide such. an: im

peller whichis well adaptedtobe easily assembled witha minimum of jigs and fixtures, which ispar ticularly arranged for easy spot welding together of all the main parts, and which can be nearly dynamically balanced as produced from the as-' sembly line.

Other advantages and objects, and the particu' lar way-sin which theaboveobiectsmay-be real ized will be apparent from. the following description taken with the accompanying drawing, which drawing and: description disclose in considerable detail only onev of the specific forms which have been made andv used with considerable success by applicants assignee.

In the drawing:

Fig. 1 is a side elevational view of an air impeller unit embodying the present invention in which portions are brokenaway to show the construction more clearly--this figure also showing a fixed inlet shroud;

Fig. 2 is a back or intake end plan view of the lower half of the impeller unit taken on. the line 2-2. of Fig. 1, the fixed inlet shroud being omitted;

Fig. 3 is a first perspective. View of a blade at the wider, back, or intake end and. looking along the nearly fiat blade face surface or from the line 3-3' in Fig. 5;

Fig. 4 is a second perspective view of the same blade looking, down on the shorter outer edge and flange and along the. nearly flat blade face surface or from the line 4-4 in Fig. 3;,

Fig. 5 is a third perspective view of the same blade looking, normal to the nearly fiat front or discharge blade face or from the line 5-5in Fig. 3;. and

Fig. 6 is a fourth perspective view of the same blade looking up on the longer inner edge and flange and along the nearly fiat blade face surface or from the line 6'-6 in Fig. 3.

The conical impeller is indicated as a whole by the numeral I, and its blades are indicated as awhole by the numerals 2'. This specific blower or fan. I is shown here in full size and substantially or as accurately as may be in the proper proportions and scale in Figs. 16, inc. This fan represents one of the production units successfully made and used by applicants" assignee. It was thought desirable to disclose at least this one unit in considerable detail, particularly as to the curved parts, and with the maiord'imensions being given, in order to enable those skilled in the art not only to make this specific design but to successfullypractice thisinvention other and varied forms byadapting and modifying these specific teachings todifferent requirements. However, it isnot intended that the detailed nature of this disclosure shall be limiting-upon the scopeof applicants invention;

As will b understood by thosefamiliar with fan design, the various: shapes and parts: taught herein, or .thefactors eifecti'ng quietness; efiiioiency and cheapn'ess (includingease'oi assembly and of dynamic balancing), are all closely interrelated and one has one oumore effects upon the other. Certain of these shapes or factors cooperate with the others in several ways to achieve the present simpl design.

As will be seen in Fig. 1, this type of fan has a generally conical-shaped discharge of air, the direction of flow of the entering and discharged air being approximately shown by the arrows in this figure. The direction of rotation is shown by the arrow A in Fig. 2. Thus it will (be apparent that this specific fan and its blades are of the backward-tipped or trailing discharge end type. Although this feature is not essential to all of the aspects or advantages of this invention, it is preferred here to achieve lower discharge tip velocities and thus a quieter running fan.

The inner hub member is designated as a. whole by the numeral 3, this hub being in th form of a truncated and axially disposed cone having its larger end towards the discharge end of the blower, and this particular design having a total apex angle of 90. It will, however, be understood that this angle may be varied within limits (about 30 either Way) while retaining most of the advantages of this invention. Of course, the form, curv and angles of the outer shroud will be similarly varied to conform with the shape of the hub member. Preferably, in order to secure a cheap and light design, this hub member 3 is in the form of a sheet metal cup having a truncated cone shape having the conical side walls or surface 4.

As is usual in conical type blowers, the close coupled coaxial motor driving the shaft is fiXed to the hub with. the electric motor usually positioned inside of the cone or cup member 3, thus producing a compact assembly. The integral truncated end of the cone 5 is suitably secured to the motor shaft-receiving means; for example, by the following structure. Member 5 is backed up or stiffened on its front face by a disk, or preferably, by the reinforcing sheet metal cone 1. The back or other side of the portion 5 is stifiened by sheet metal disk 8. The solid shaftreceiving member 9 has a reduced front end portion IE! fitting in and through the centrally located hole 6 in portion 5 and also through the corresponding same sized holes through members I and 8. The front or discharge end II of portion I is formed so .that it can be bent or forced over to firmly grip or clamp members 5, 'I and 8 between the two enlarged portions thus formed ateither end of portion ID. This cheap assembly method also assures the coaxial alignment important to proper dynamic balance. The memiber 9. has the usual hole I2 there-through to receive the motor shaft (not shown) which is held by means such as the set screw I3.

The outer shroud ring of this specific design has the largest diameter of 6%" and a depth from front to back, from discharge end to intake end, of 2 Thus this fan is of a nominal 7"v size. Of course, ring I is concentric with and uniformly spaced about conical hub 3.

I As shown, this shroud ring I5 is sheet metal, generally conical in shape, and curved for smooth air flow therethrough. Specifically, in axial crosssection it is curved convex inwardly. Although a uniform curve might be used to advantage theoretically, and although a plain conical section would b operative with more air turbulence, yet as a practical matter the best results or operation and ease of construction have been obtained with the ring I5 formed of an inlet portion I'i, which is here about /2 wide, and which is substantially cylindrical in appearance. Actually, however, the portion I1 diverges very slightly toward the inlet end; that is, it is slightly conical, to cooperate or form a part-of the resilient snap-on feature described in greater detail below. The general y cylindrical portion I1 provides a straight or axial flow entrance to the blades 2.

Thus, this portion I1 is intended to be used with a fixed or non-rotating inlet shroud such as 50, as shown in Fig. 1. This inlet 50 has its discharge end substantially cylindrical to match portion I1 and its inlet end diverging along a smooth air flow curve to reduce turbulence of the air being drawn into the fan. The member 5i] may be mounted or secured in place by various means, such as screws or the like, through the integral bent-over flange portion 5| which may, if desired, be at its inlet end. In order to reduce the depth of the fan from front to back and to reduce the cost, it will be found desirable to have inlet portions 50 separate or not forming a part of the rotary ring I5. This construction also permits a longer inlet shroud 50. It is also desirable since som sort of fixed inlet guide is generally used in any case.

The discharge end I6 of ring I5 is here of conical form and of slightly less than width from front to back. However, if desired, the intermediate curved portion I8 may be continued through to the discharge end. As shown, the conical portion I6 has a somewhat smaller apex angle than cone 4 so that walls I6 converge with respect to walls 4. The intermediate portion I8 is curved and merges into the two portions I6 and I1. As shown here, member I8 is curved on a radius of 1 /2".

As noted above, the blades 2 are preferably, but not necessarily, of the backward-tipped type. It has also been found quite desirable to form these blades 2 so that they are perpendicular to the conical surface 4 at any point along their length of intersection with 4. That is, the blades are slightly curved so that at any point of the intersection of the blades with the conical hub surface, a straight line element of the blade will be normal or perpendicular to the conical surface even though the flange of the blade is bent over less than However, although desirable in giving a simpler structure and quieter fan, this feature is not essential to all aspects of this invention, such as the snap-on feature and other features, as will be apparent.

Bearing in mind that the blades 2 are of the backward-tipped type and are perpendicular to the conical surface 4 (that is, as close to perpendicular as is practical for large scale manufacture in light sheet metal), the exact shape or formation of these blades will be Well understood by a comparison of the six different full-sized views given in Figs. 1-6, inc. Each blade 2 has a front or discharge face 20, a back or intake face 2I, a back or intake end 22, a front or discharge and trailing end 23 (22 and 23 being out straight for convenience), the curved radially inner and longer edge 24, and short curved radially outer edge 25.

Also, each blade has an integral flange having an outer surface 26 and an inner surface 25, this flange extending along the entire length of edge 24 and being bent over toward the front face 20 through an angle of less than 90. This flange 26. has its front end cut off on an angle, as seen at 21, to lie along the end or face of portion 24, and its other or back end 28 is cut off normal to its free edge 29. The shorter or radially outer edge 25 is also curved and has, extending along its entire outer length, a flange-having the radially outer surface 32 and a radially inner surface 32'. The free edge of this flange is seenat 36, and its ends 34 and 35 are cut off as shown, end 35 being arranged to lie along or parallel with the inlet of ring I5. Flange 32 is also bent through an angle of less than 90. It is important to note that these flanges 26 and 32 are oppositely directed, which permits them to be bent through angles of less than 90. This is important in that it requires less deformation of the metal and permits. a simpler die when these blades are made by a punching operation, as is preferred and used in production of the present blades of sheet metal. Also, these oppositely-directed flanges give easier access for the Welding electrodes since it is preferred to assemble this fan by welding, as explained in greater detail below.

These flanges, particularly since they are bent along the curves 24 and 25, also materially stiffen the blades and eliminate the necessity for embossed ribs or other stiffening means, thus permitting simpler dies' and smoother air flow.

As best shown in Fig. 5, these nearly flat blades are of a generally trapezium shape in face outline. As seen in several figures, these blades are only slightly curved, this small amount of curvature being in part due to the blades being formed to be perpendicular to cone surface 4, instead of designed so that their elements are parallel to the. axis of rotation, and also to the fact that the curve 24 (that is, the line of intersection of a blade along cone 4) is an unwrapping curve or, specifically, an involute of a circle as specifically shown in the drawing, particularly the full sized accurate Figures 3 to 6 inclusive. Thus it will be seen that the slightly curved blades have a smoothly progressively decreasing curvature with the minimum curvature at the discharge or outlet end of the blower. The fact that these blades are nearly flat makes them easier to form.

Athough it may be secured together in various ways, this fan is particularly designed to be assembled by spot welding, the three weld spots for the inner flange 26 being shown at points 4| in the several figures, and the two axially spaced welds for the outer flange 32' being shown at points 42. It is to be noted that the two spaced welds 42 fall on either side of the joining or merging point of portions I1 and I8 of the ring I5. Since IT has a slight reverse slope to portion I8, this gives strong assembly since there is a Weld on either side of the central or rocker point where portions I1 and I8 meet.

Since in a fan of this type the major air flow is in the radially outer portions, the exact shape of the cone 3 is not as important to smooth air flow as the shroud or ring I5. Thus surface 4 is made exactly conical since it is much easier to locate and position the blades 2 upon an exactly conical surface by the usual jigs and fixtures. However, it will be seen that 3 need not be made exactly conical.

Although the several parts of this fan may be made of various materials and secured in Various Ways, sheet metal is preferred, and here the several parts are made of steel. The cone 3 and the shroud I5 are made of gauge cold rolled steel, and the blades 2 are made of 22 gauge cold rolled steel. Members 3 and I5 have been made-by spinning, but in larger production it is desirable to make them by drawing, the blades beingpunched by dies, as mentioned above.

As noted above, this design is arranged particularly for an easy welded assembly in which the blades 2 are held in position with respect to the conical surface 4 by a suitable jig and are welded in place at the spots 4|, as shown. The welding electrodes can be easily inserted from the discharge end. In this design, ring I5 is forced over the blades axially from the intake end and snaps into place in one definite axial position with respect to the cone 3 Where it is firmly and resiliently held against axial displacement in either direction and, in fact, so firmly held that the fan may be satisfactorily run without fastening ring I5 by welding or other means. This resilient snap-on action accurately positions ring I5 at the point for proper dynamic balance and proper air flow, thus eliminating the necessity for any jig, fixture, or the like, to set the axial position of ring I5.

This resilient snap-on action is obtained by the cooperation between the shapes of the resilient blades 2 and the resilient ring I5. The end portion near 35 of outer flange 32 is formed in the dies so that it projects out a little further than is necessary to neatly fit against portion ll of ring I5. This projecting portion at 35 firmly and resiliently clamps against the above-described slightly outwardly tipped portion I1 which, it will be noted extends outwardly in the opposite fashion to portion I3 so that ring I5 is thus firmly held against axial movement in either direction with sufficient force so that it cannot be rotated. Further, this position is quite accurate to properly locate ring I5 for commercially satisfactory dynamic balance of the whole fan.

As ring I5 is forced on over the blades, the flanges, at their ends 35, bend inwardly, but most of the elastic motion is taken by the blades bending as a whole. As will be seen in Figs. 1 and 2, the blades will bend inwardly away from their inner flanges 26. This, of course, is accompanied by a certain elastic deformation of ring I5, which will be smaller since ring I5 is well stiff-- ened because of its curved cross-sectional shape. As the ring comes into its final position, the blades spring out slightly and the resulting or normal elastic deformation is only enough to hold ring I5 firmly.

Thus it will be apparent that the blades are radially resilient or have a radial component of resiliency or resilient movement to cooperate with, or to permit, this snap-on feature. As will be seen in Figures 1 and 2, the blades are not radial and hence these relatively thin elastic or resilient metal blades may be elastically bent or flexed to produce this resilient inward and outward radial motion at their outer end portions.

It will be apparent, of course, that a snap-on holding or positioning means of this type may be provided in numerous other ways.

After ring I5 is in place, the weld spots 42 are applied to give extra strength and to prevent accidental disassembly. It will be noted that electrodes may be entered one from each end or both from either end, whichever is most convenient.

Another feature to be noted in this design is that all of the weld spots M and 42 carry little or no load because of this snap-on feature, as

noted above, and also, because of the particular form of the blades, which are so arranged that the loads due to centrifugal force and air pressure tend to rotate or twist the blades in such fashion that they are locked more tightly between conical surface 4 and ring l5.

It will also be noted that the slight distortion of the metal due to spot welding will be mostly taken up between the blades and the outer ring a substantially constant cross-sectional area for the air going through the fan between these surfaces, and thus a substantially constant velocity. Accordingly it is thought desirable to have portions I6 and I8 of ring l converge with respect to surface 4.

As noted above, it is desirable (although not' necessary to all the benefits of this invention) that the blades 2 intersect the surface 4 along the line 24 on an involute curve, as shown.

While this impeller may be defined as an air impeller, or the like, for the sake of brevity in the specification and claims, it is to be understood that this is intended to include other gases or fluids.

It will, of course, be well understood by those skilled in this art that various other shapes, arrangements or materials may be employed within the spirit of this invention and the scope of the claims.

We claim:

1. A rotary impeller comprising a hub consisting of a central axially aligned sheet metal cup forming a truncated cone, an outer shroud consisting of a concentric, generally conical, sheet metal band ring, a plurality of slightly curved and thus nearly flat resilient sheet metal blades, extending non-radially therebetween so that said non-radial blades may be flexed as a whole to give a radially resilient motion at their outer ends, each blade having oppositely-directed, integral flanges bent over through less than a right angle along the entire length of its inner and slightly curved outer edges, the generally conical band ring and the slightly curved, bent over outer edges of the resilient blades forming correspondingly curved, inter-engaging surfaces whereby the shroud may be snapped on and thus resiliently held in place on the blades and in operation by said radially resilient motion, and

axially spaced welds securing each of said flanges to said conical hub and shroud, respectively, said bent over flanges stiifening said nearly flat blades to eliminate the necessity for other stiffening means, such as embossed ribs, and said flanges being so disposed as to permit easy welding in assembly.

2. A rotary impeller comprising a central hub member, a plurality of blades secured thereto and being radially resilient by flexing for an in or out radial resilient motion of their outer ends, and an outer shroud member about said blades and engaging their outer ends, the outer ends of said blades and said shroud member having inter-engaging curved surfaces so that said shroud member is firmly held on said blades by their said radial resiliency and may be elastically snapped on.

3. A rotary air impeller having a conical discharge and comprising a general conical hub, a plurality of blades secured to and about said hub, and a generally conical outer shroud ring about said blades, said blades being of thin resilient material, extending non-radially, and being shaped and arranged to be flexed so that their outer ends have a radial component of resiliency, and the outer ends of said blades and the inner surface of said shroud ring having interfitting engaging and retaining surfaces such that the shroud ring can be axially forced onto said blades by flexing them for radial resilient motion of their outer ends and to firmly retain said shroud ring in position.

4. The organization set forth in claim 3 in which the inner surface of said shroud ring, in any axial cross-section, is convex with both its intake and its discharge end portions diverging from the axis of rotation, and portions of the outer end of each blade are shaped to resiliently engage the intake and the discharge end portions of said ring to provide said interfitting engaging and retaining surfaces.

5. A rotary impeller comprising a generally conical hub member, a plurality of elastic sheet metal blades secured to said hub member and extending generally non-radially with respect to the axis of rotation, each blade having an integral stiffening and securing flange bent over along its outer edge, a generally conical, outer shroud ring about said blades and their outer edge flanges, said ring having re-entrant portions, one axial end portion of each of said elastic metal flanges being originally permanently bent out beyond its final position to flex resiliently and press radially out against said re-entrant portions of said shroud ring to lock said ring in position for proper dynamic balance.

PHILLIP A. MULLER.- LACHLAN W. CHILD. 

